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Photovoltaic panels are used to generate a current, or voltage, when exposed to visible light to convert sun energy into electricity.

The Photovoltaic panels are very expensive and naturally can not produce any current, in times of low light or darkness.  As a result they require the installation of Lithium batteries and the resulting hardware needed, to store the electricity if the electricity is needed at times of low light or darkness.

The current cost of installing a Photovoltaic system, to produce the electric required to heat enough domestic hot water for a family of four, is around $36,000,  Photovoltaic panels are thus not currently an economical alternative, for the average home-owner, vis-a-v any of the other readily available sources of energy